The members of seventeen families, comprising seventy-nine normal volunteers, having no clinical evidence of disease, were examined for multiple ribonuclease activities using polynucleotide-polyacrylamide gel electrophoresis. Gels (6.5%) were prepared containing polyadenylic acid (.05%). Serum samples (15 microliters) were electrophoresed using conditions under which enzyme catalyzed hydrolysis of the polynucleotide did not occur (pH 8.6). After electrophoresis, gels were incubated and stained, revealing RNase activities as colorless bands in otherwise purple gels. The high resolution obtained with this technique enables 22 distinct activity bands to be visualized. Although no two individuals had identical activity patterns, a statistical profile of a normal serum pattern was obtained. These studies are the basis for examination of activity patterns of indviduals having leukemia. Serum RNase patterns of patients change in response to treatment of disease. Coincident with treatment, certain enzymes appear or disappear, and the intensities of some bands undergo marked alterations.